A fuel cell system is known in the art, which system is provided with: a cell for fuel cell, which cell has a membrane electrode assembly which is provided with an electrolyte and a cathode and anode which are respectively arranged at two sides of the electrolyte and an oxidizing gas passage which feeds an oxidizing gas to the cathode; an oxidizing gas feed path which is connected to an inlet, of the oxidizing gas passage; and an oxidizing gas feeder which is arranged in the oxidizing gas feed path and feeds oxidizing gas to the cathode.
If moistness of a cell for fuel cell, in particular an electrolyte or electrodes, becomes lower, power generation quantity or efficiency of the cell is liable to become lower. Here, the moistness of the cell is expressed by an output current value of the cell. That is, as the moistness of the cell becomes lower, the output current value of the cell becomes smaller. On the other hand, when oxidizing gas is sent to the cell, the oxidizing gas which flows out from the cell or cathode off-gas carries off moisture from the cell. If the amount of oxidizing gas which is sent to the cell becomes smaller, the amount of moisture which is carried off from the cell becomes smaller.
Therefore, a fuel cell system is known in the art, in which the oxidizing gas feeder is controlled to reduce the amount of oxidizing gas which is sent to the cell if the output current value of the cell is smaller than a predetermined threshold current value (see PTL 1). As a result, the amount of moisture which is carried off by the cathode off-gas is decreased and therefore the moistness of the cell is gradually raised, that is, is restored.